Carbon nanotube (CNT) yarns are novel CNT-based materials that extend the advantages of CNT from the nanoscale to macroscale applications. Herein we have modeled the electrical properties of carbon nanotube yarn as a function of temperature and magnetic field. The conductivity was well explained by 3D Mott Variable Range Hopping (VRH) law at T < 100 K. The hopping effective dimension is reduced with increasing of magnetic field. Negative magnetoresistance (MR) was observed at different magnetic field range. A quadratic MR was found at small magnetic fields up to B D2 , where a deviation occurred from the quadratic magnetic field dependence of the MR. In the intermediate magnetic field region, the negative MR shows linear magnetic field dependence up to the magnetic crossover field of B D1 . It was found that physical parameters such as the localization length and the density of states at the Fermi level are temperature and magnetic field dependent. In addition, a general scaling behavior was found for the MR as a function of (B/B*) 1/3 , where B * is a crossover magnetic field.